The present invention generally relates to a semiconductor memory device having an aluminum-based metallization film and a refractory metal silicide-based metallization film.
Generally, in a conventional field effect transistor, source and drain regions are formed by a self-alignment process in which a gate electrode is used as a mask film. Therefore, such a gate electrode is formed by using polysilicon having a high heat-resistant property. Polysilicon has a disadvantage in that it's value of electrical resistance is higher than that of an alloy of aluminum-silicon, which is used for forming source and drain electrodes. As in a case of a dynamic random access memory (DRAM) device where a gate electrode of a polysilicon film is used as a word line, a metallization film of an aluminum-silicon alloy is formed on an insulating film positioned in a vicinity of a top surface of the DRAM device, and is connected to the gate electrode of the word line at a suitable position. That is, the aluminum-silicon metallization film is used for improving conductivity of the gate electrode. However, an aluminum-silicon alloy has a disadvantage that heat-resistance is low.
It is also known to use, as a metallization film, a polycide film which is a stacked layer consisting of a polysilicon film and a refractory metal silicide film. Compared with an aluminum-silicon metallization film, a polycide film has a disadvantage of high electric resistance and has advantages of high heat-resistance and high resistance to electromigration and stress-migration.
As can be seen from the aforementioned explanation, metallization materials have both advantages and disadvantages.
Recently, a size of a semiconductor chip of the DRAM device is limited in view of a size of a package which accommodates the semiconductor chip. For example, a standard package has a width (a short side) of approximately 7.5 (mm) (300 (mil)). Therefore, a semiconductor chip is necessarily of a rectangular shape. As a result, in a case where sense amplifiers, bit drivers and column decoders are arranged along the short side of the chip, a bit line pitch which defines a distance between centers of neighboring bit lines, must be necessarily reduced, compared with a word line pitch which defines a distance between centers of neighboring word lines arranged in a direction of a long side of the chip. On the other hand, in a case where a row driver and a row decoder (word decoder) are arranged in the short-side direction of the chip, the word line pitch must be made smaller than the bit line pitch. Therefore, it is required to provide a metallization structure suitable to the rectangular semiconductor chip.